1,1,1-Trifluoroethane (143a) is a hydrofluorocarbon (HFC) with zero ozone depletion potential (ODP). The product was described earlier in the literature as an undesirable co-product from processes involving hydrofluorination of 1,1-dichloroethylene (VDC, 1130a) or 1,1,1-trichloroethane (140a). While methods are known for synthesizing 143a, there is a need for a simple, convenient, economical, industrial process for the manufacturing of 143a. The present invention provides a new practical process for the production of 143a with very high conversion and very high selectivity (both over 99%) for 143a.
In U.S. Pat. No. 3,231,519, issued Jan. 28, 1966 and assigned to Union Carbide Corporation, a catalyst composed of coprecipitated iron hydroxide and rare earth oxide, such as dysprosium hydroxide, and zirconium oxide was used to hydrofluorinate 140a to a mixture of 143a, 142b and 1130a. Thus, when hydrogen fluoride (177 g, 8.85 moles) and 1,1,1-trichloroethane (541 g, 4.05 moles) were vaporized over 150 milliliters of the catalyst over a three to four hour reaction period at a temperature of 230.degree.-260.degree. C., to give 1,1,1-trifluoroethane (122 g, 1.45 moles); 1-chloro-1,1-difluoroethane (33 grams, 0.328 moles); 1,1-dichloroethylene (157 g, 1.62 moles) and a small amount of 1-chloro-1-fluoroethylene. The latter two products, 1130a and 1131a, are a waste co-product; conversion was 83.9% and selectivity for 143a was 42.67% under these conditions. Catalysts claimed in this patent are a combination of iron oxide, rare earth oxide, and zirconium oxide. The lifetime of the catalyst was not reported.
U.S. Pat. No. 3,287,424, issued Nov. 22, 1986 and assigned to Stauffer Chemical Company, discloses the hydrofluorination of 1,1,1-trichloroethane (140a) to 1,1,1-trifluoroethane (143a) in a batch process, using arsenic trifluoride as a fluorinating agent and antimony pentafluoride as a catalyst. In Example 3, a mixture of arsenic trifluoride (333.25 grams, 2.53 moles) and antimony pentafluoride (29.9 grams, 0.14 moles) was reacted with methylchloroform (133 g, 1 mole) at 45.degree.-50.degree. C. to produce 1,1,1-trifluoroethane (63 g, 0.75 moles). The fluorinating agent, AsF.sub.3, is a highly toxic material and is an expensive reagent for industrial applications.
U.S. Pat. No. 3,803,241, assigned to Dynamit Nobel AG, uses a catalyst composed of chromium (III) chloride supported on alumina, prepared by soaking aluminum oxide pellets in CrCl.sub.3.6H.sub.2 O solution (31 wt. %). The catalyst was dried at 200.degree. C. using nitrogen or air, followed by HF activation at 250.degree. C. for 2 hours. In Example 1, following the HF activation, a gaseous stream of 1,1-dichloroethylene and hydrogen fluoride in a molar ratio of 1:3.5 at 150.degree. C. was passed over the catalyst bed at 150.degree. C., to yield 98.8 volume % of 1,1,1-trifluoroethane, 0.2 volume % of 142b, 0.2 volume % of 141b and 0.8 volume % of 1,1-dichloroethylene. After running for quite some time (exact running time not reported), the catalyst was regenerated by heating for 10-15 days. No experimental details were provided on how the catalyst was reactivated nor was there evidence that the catalyst performance improved after the treatment. Although the selectivity and conversion were very high, the catalyst required a very long time for regeneration, which is not practical for industrial applications.
In U.S. Pat. No. 3,833,676, it is disclosed that hydrofluorination of methyl chloroform in a liquid phase batch process can produce very low levels of 1,1,1-trifluoroethane (Example 2). In this example, methyl chloroform (3.73 grams) and hydrogen fluoride (17 g) (molar ratio of HF:methyl chloroform=30.3:1) were mixed together in a stainless steel reactor at 110.degree. C. for 2 hours to produce 2.3 mole % of 141b, 95.5 mole % of 142b and 2.1 mole % of 143a. This process is a liquid phase process and requires very long contact time, which means that it is much less productive compared to continuous gas phase processes.
In U.S. Pat. No. 3,836,479, Example 1, a catalyst composed of boric acid (0.18 kg) mixed with pseudoboehmite alumina (1.2 kg) was prepared and activated using hydrogen fluoride at 350.degree. C. using 2 mole/hr HF and 1 mole/hr nitrogen. After the catalyst was activated, a mixture of HF (0.75 mole/hr) and vinylidene fluoride (feed rate not reported) was passed over the catalyst at room temperature to produce 100% conversion to 143a. (Example 12) The feed stock of this process, 1,1-difluoroethylene, is an expensive compound for industrial application, and it is expected that 143a produced using this process will be expensive.
A bismuth containing catalyst supported on alumina was prepared in Example 1 of U.S. Pat. No. 3,904,701 by soaking alpha-alumina (650 g) in a mannitol solution of Bi(NO.sub.3).sub.3.5H.sub.2 O (153 g). The catalyst was dried at 80.degree. C. for one hour. Subsequently it was activated at 250.degree. C. using a mixture of HF and air. Then a gaseous mixture of 1 part dichloroethylene and 3.2 parts of HF (Example 1) was passed over the catalyst bed at 180.degree. C., with 18 seconds contact time. Analysis of the product obtained indicated that conversion was 99.9%; selectivity for 143a was 99.8% and for 142b it was 0.2%. In all the examples reported in this patent, halogenated alkenes were used as the feed stock. E.g., in Examples 1, 3, 4 and 5; 1,1-dichloroalkene was used as the starting material; in Example 2, vinyl fluoride monomer was used as the organic substrate. The composition of the catalyst of this patent (Bi/Al.sub.2 O.sub.3) is totally different from that of the catalyst of the present invention. This patent also discloses an improved regeneration process for the above catalyst, by heating the deactivated catalyst in air at a temperature of about 350.degree.-450.degree. C. This regeneration process is claimed in related U.S. Pat. No. 3,965,038.
A continuous liquid phase process for the hydrofluorination of methylchloroform to the mixture of products 141b, 142b and 143a is disclosed in U.S. Pat. No. 4,091,043. The process requires continuous feed of antimony pentachloride in the presence of organic solvent. This will require additional separation equipment to separate the antimony catalyst and the organic solvent, which is troublesome on the industrial scale. The best result for CH.sub.3 CF.sub.3 selectivity (82.6%) was obtained when the reactor was initially charged with SbCl.sub.5 (52.2 mole %) and 0.76 moles of the solvent 1,1,2-trifluoro-1,2,2-trichloroethane. The feed rate of methylchloroform was 0.76 mole/hour; for HF it was 2.32 mole/hour. At 28.degree. C., conversion was 93%, while selectivity for 143a was 82.6%. Selectivity was 17.1% for 142b and 0.3% for 141b. A similar process was described in Atochem S.A.'s European Patent Publication No. 0 421 830 A1, which uses a combination of SbF.sub.5 and chlorine gas as a catalyst for a HF/methylchloroform process. The percent selectivity of 143a varied between 1% to 10.3%, depending on the processing conditions. Again, this process requires recovery of the antimony catalyst. In the absence of chlorine gas, the active catalytic species, Sb(V), was reduced to the inactive catalyst species, Sb(III).
In U.S. Pat. No. 4,147,733, Example 2, a catalyst composed of alumina coated with 12 percent by weight of Cr.sub.2 O.sub.3 and 6% of NiO, was used to hydrofluorinate chlorinated aliphatic hydrocarbons to the corresponding fluoride using aqueous HF, e.g. at 420.degree. C. Feeding a mixture of 38% aqueous HF and 1,1-dichloroethylene vapors at a 3:1 molar ratio of HF/VDC, gave a total conversion of 16.3% to fluorinated product. The selectivity for 143a was 54.1 mole %, while it was 21% for 1-chloro-1-fluoroethylene and 20.4% for vinylidene fluoride. This process requires the use of aqueous HF as a feed stock, which is known to be very corrosive compared to anhydrous HF gas. Furthermore, the presence of the fluoro-olefin as impurity in 143a is undesirable for either refrigerant applications or foam blowing agent applications.
1,1,1-Trifluoroethane was also reported as a major co-product, during the fluorination of vinylidene fluoride, using activated carbon, in U.S. Pat. No. 4,937,398. The process was directed towards the preparation of 1,1,1,2-tetrafluoroethane. Instead, 143a was the major product. The latter product was suggested to be obtained from a process involving HF addition to vinylidene fluoride. HF was disclosed to be generated by hydrolysis of fluorine gas by the moisture on the surface of activated carbon, e.g., when VF.sub.2 (8 cc/m) mixed with nitrogen (50 cc/m) was slowly fed over activated carbon (40 grams, saturated with 6 wt % of fluorine gas). At 50.degree. C., conversion was 100% and selectivity for 143a was 82%. Selectivity for 1,1,1,2-tetrafluoroethane (134a) was 18%. The implementation of this process for the production of 143a can be a very difficult task, because fluorine gas addition to olefin is a highly exothermic process.
In U.S. Pat. No. 5,008,474, Example 1, hydrofluorination of 1,1-dichloroethylene in the presence of tin tetrachloride as a catalyst, in a batch liquid phase process, produced 143a in small quantities. E.g., when 5.16 moles of 1,1-dichloroethylene, 16.05 moles of HF and 0.25 moles of SnCl.sub.4, were mixed together under continuous stirring, analysis of the product formed showed the following composition: 143a (2.1 mole %), 142b (26.7%), 141b (64.8%), vinylidene chloride (4.1%), 1,1,1-trichloroethane (0.8%) and oligomeric material (1.4%). In Examples 2-4, the yields of 143a were even lower. Thus, the yield of 143a from this process is not high enough for it to be utilized as an industrial process.
European Patent Publication 0 486 333 A1 (134a) discloses the manufacture of 1,1,1,2-tetrafluoroethane by the vapor phase hydrofluorination of 1-chloro-2,2,2-trifluoroethane (133a) in the presence of a mixed catalyst composed of oxides, halides and/or oxyhalides of chromium and nickel on a support of aluminum fluoride or a mixture of aluminum fluoride and alumina. In (comparative) Example 3, it is taught that the presence of nickel, together with chromium, in the catalyst, enhances both the activity and stability of the catalyst.
International Patent Publication W093/25507 is directed, more broadly, to the vapor phase hydrofluorination of a halocarbon (having at least one halogen other than fluorine) with anhydrous HF, at a temperature above 200.degree. C., in the presence of a catalyst comprising a chromium compound and at least one transition metal compound selected from the oxides, halides and oxyhalides of nickel, palladium and platinum. The catalyst may be unsupported, supported or mixed with an appropriate bonder. Suitable supports are taught to include aluminum oxide, aluminum fluoride, aluminum oxyfluoride, aluminum hydroxyfluoride and carbon. This publication also teaches the importance of the presence of nickel in the catalyst, together with chromium, in order to obtain high rates of conversion and prolonged catalyst activity. 1,1-difluoro-1-chloroethane (142b), the starting material of the process of the present invention, while within the generic disclosure of this publication, is not expressly mentioned therein.
The prior art also describes processes that produce 143a which are based on hydrofluorinating either 140a or 1130a. The first compound (140a) is expected to be regulated by the U.S. federal government in the near future. The second compound (1130a) is known to undergo cationic polymerization to produce low molecular weight polymer and thereby deactivate the catalyst. (See McBeth et al., J. Chem. Soc., Dalton Trans., (1990) 671.) In many cases, it is believed that, if an inhibitor is added to the feed stream, it is likely to poison the catalyst. There is need for a simple, convenient and economical process for the production of 143a that avoids the foregoing problems.